All the informarion Solterra had was that Aldran had the larger army, and was at an age that would have efficient enough battle strategy without needing to have been in wars. 

It was thought about afterward when Solterra received more information that he regretted the decision, also the fact he didn't know about the son causing a martyr effect. 

I don't make arguments based on OOC information. To that extent, Solterra has a great pain that he has to go to war with Cole.